Twilight OI 6300 Å Airglow Measurement Using a High Dispersion Monochromator

Abstract

The OI 6300 Å airglow in the morning twilight was observed with a high dispersion Ebert spectrometer. The 6300 Å emission could be detected against the background continuum due to Rayleigh scattering of the solar radiation with good accuracy for the solar zenith angle (SZA) larger than 96°. The O₂ photodissociation may be the main excitation process for SZA=102°-98°; a theoretical calculation based on this excitation process can reproduce the observed 6300 Å intensity. The emission intensity observed shows a long-term variation in correlation with the solar activity, which may be caused by the variation of the thermospheric O₂ density due to the variation of the thermopause temperature. A seasonal variation of the emission intensity, which shows large enhancement in winter, would be ascribed to the additional excitation by the local and conjugate photoelectron.